ESD protection device

ABSTRACT

An ESD protection device includes: a first insulating layer ( 2   a ); a second insulating layer ( 2   b ) stacked on the first insulating layer ( 2   a ); a first via conductor ( 6   a ) extending through the first insulating layer ( 2   a ) in a thickness direction; a discharge gap portion ( 10 ) provided so as to be in contact with the first via conductor ( 6   a ), between the first insulating layer ( 2   a ) and the second insulating layer ( 2   b ); a first wiring line ( 7   a ) that is arranged on a surface of the first insulating layer ( 2   a ) opposite to the discharge gap portion ( 10 ) and that is electrically connected to the first via conductor ( 6   a ); and a second wiring line ( 7   b ) that is arranged on one surface of the second insulating layer ( 2   b ) and that includes a portion facing the first via conductor ( 6   a ) with at least the discharge gap portion ( 10 ) interposed therebetween.

BACKGROUND OF THE DISCLOSURE

Field of the Disclosure

The present disclosure relates to an ESD protection device. “ESD” standsfor electro-static discharge. ESD is a phenomenon in which a strongdischarge is generated when a charged conductive object, for example, ahuman body, comes into contact with or comes sufficiently close toanother conductive object. An “ESD protection device” is a device forallowing an electric charge to flow to GND and protecting a circuit,when an electrostatic discharge is generated.

Description of the Related Art

These days, ESD protection devices for protecting electronic apparatusesfrom an electrostatic discharge are widely used.

An example of a circuit where an ESD protection device is used isillustrated in FIG. 13. A circuit to be protected (hereinafter called a“protected circuit”) 502 is electrically connected to a terminal 503.The protected circuit 502 is, for example, an integrated circuit (IC).The terminal 503 represents a portion where a conductor or the like isexposed to the outside in a connector or the like. An ESD protectiondevice 501 is connected to an end of a wiring line branching from amidpoint of a wiring line connecting the protected circuit 502 and theterminal 503 to each other. The ESD protection device 501 and theprotected circuit 502 are separately grounded. As illustrated in FIG.13, in a normal state, the discharge electrodes within the ESDprotection device 501 are in a state in which a current does not flowbetween the discharge electrodes. When an ESD is generated as a resultof, for example, a human body coming into contact with or comingsufficiently close to the terminal 503, a high voltage is applied to theterminal 503. At this time, without taking any steps, an overvoltage isapplied to the protected circuit 502 and a current will flow asindicated by an arrow 92. However, when a discharge is generated betweenthe discharge electrodes of the ESD protection device 501, a currentwill flow in a direction indicated by an arrow 91 due to the dischargeand, hence, an overvoltage is not applied to the protected circuit 502.In other words, the protected circuit 502 is protected.

For example, Japanese Unexamined Patent Application Publication No.2009-238563 (Patent Document 1) discloses a structure called an“overvoltage protection component” in which a hollow functioning as adischarge portion is formed inside a base body formed of an insulatorand discharge electrodes face each other within this hollow. It isdisclosed in Patent Document 1 that the discharge electrodes are formedby printing, plating, or the like.

For example, Japanese Unexamined Patent Application Publication No.2001-217057 (Patent Document 2) discloses a structure called a“chip-type surge absorption device” in which internal electrodes faceeach other inside an insulating ceramic sintered body. A discharge spaceis formed so as to be interposed between the internal electrodes. It isdisclosed in Patent Document 2 that the discharge space is filled with acarbon paste by using screen printing, and the carbon paste is burntdown at sintering time.

-   Patent Document 1: Japanese Unexamined Patent Application    Publication No. 2009-238563-   Patent Document 2: Japanese Unexamined Patent Application    Publication No. 2001-217057

BRIEF SUMMARY OF THE DISCLOSURE

In Patent Document 1, since the discharge electrodes are formed byprinting, plating, or the like, the discharge electrodes are thinconductive layers attached to the surface of an insulator. At adischarge time, electrons collide with this discharge electrode and,hence, the discharge electrode may become detached due to the impactcaused by the collision of the electrons. In Patent Document 1, a cavityis provided in an insulating sheet, the cavity is filled with an acrylicresin as a discharge portion forming material, and the acrylic resinevaporates in a firing process to form a hollow. Since the hollow isformed in this way and the discharge electrodes facing each other withthe hollow interposed therebetween are formed by printing or the like, adecrease in the gap between the discharge electrodes, i.e., asufficiently narrow gap, was not realized.

Also in Patent Document 2, since the chip-type surge absorption deviceis formed by using a printing method and a green sheet method, asufficiently narrow gap between the discharge electrodes was notrealized.

Hence, it is an object of the present disclosure to provide an ESDprotection device that realizes a further reduction in a gap between thedischarge electrodes and that can alleviate a problem in that thedischarge electrodes become detached.

To accomplish the above object, an ESD protection device based on thepresent disclosure includes: a first insulating layer; a secondinsulating layer stacked on the first insulating layer; a first viaconductor extending through the first insulating layer in a thicknessdirection; a discharge gap portion provided so as to be in contact withthe first via conductor, between the first insulating layer and thesecond insulating layer; a first wiring line arranged on a surface ofthe first insulating layer opposite to the discharge gap portion andthat is electrically connected to the first via conductor; and a secondwiring line arranged on one surface of the second insulating layer andincluding a portion facing the first via conductor with at least thedischarge gap portion interposed therebetween.

According to the present disclosure, a further reduction in a gapbetween discharge electrodes is realized and a problem in that thedischarge electrodes become detached can be alleviated.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a sectional view of an ESD protection device in a firstembodiment based on the present disclosure.

FIG. 2 is an explanation diagram of a state of the ESD protection devicein the first embodiment based on the present disclosure before layerstacking.

FIG. 3 is a sectional view of an ESD protection device in a secondembodiment based on the present disclosure.

FIG. 4 is an explanation diagram of a state of the ESD protection devicein the second embodiment based on the present disclosure before layerstacking.

FIG. 5 is a sectional view of an ESD protection device in a thirdembodiment based on the present disclosure.

FIG. 6 is an explanation diagram of a state of the ESD protection devicein the third embodiment based on the present disclosure before layerstacking.

FIG. 7 is a sectional view of an ESD protection device in a fourthembodiment based on the present disclosure.

FIG. 8 is a sectional view of an ESD protection device in a fifthembodiment based on the present disclosure.

FIG. 9 is a sectional view of an ESD protection device in a sixthembodiment based on the present disclosure.

FIG. 10 is an explanation diagram of a state of the ESD protectiondevice in the sixth embodiment based on the present disclosure beforelayer stacking.

FIG. 11 is a sectional view of an ESD protection device based on anexisting technology.

FIG. 12 is an explanation diagram of a state of the ESD protectiondevice based on the existing technology before layer stacking.

FIG. 13 is a circuit diagram in an example of a situation in which anESD protection device is generally used.

DETAILED DESCRIPTION OF THE DISCLOSURE

When an ESD protection device is produced by stacking insulating sheetson top of one another, a discharge portion may be formed by providing ahollow having a thickness of a single insulating sheet. However, withthis configuration, the thickness of a hollow is approximatelydetermined by the thickness of the insulating sheet, and a sufficientlynarrow gap cannot be realized.

A gap may also be formed such that by arranging neighboring dischargeelectrodes on the same surface and forming a gap between the dischargeelectrodes arranged in the left-right direction. However, in the case inwhich the discharge electrodes described above are formed by printing,the outlines of the discharge electrodes planarly viewed are not stabledue to a blur in printing. Hence, a large clearance is needed to avoid ashort circuit and, therefore, a small gap cannot be precisely formed.Specifically, when the intended gap is a gap smaller than about 20 μm,it was difficult to form the gap in a stable and accurate manner.

On the other hand, when a layer is formed by printing, the variation ofthe thickness of the layer is small and a blur in printing is seldomobserved in the thickness direction. The thickness of a layer formed byprinting can be controlled by the amount of the solid component of apaste or the ejected amount of a paste.

In consideration of these situations, the inventor has accomplished thefollowing disclosure.

First Embodiment

An ESD protection device in a first embodiment based on the presentdisclosure will be described with reference to FIG. 1.

As illustrated in FIG. 1, an ESD protection device 101 in the presentembodiment includes a first insulating layer 2 a, a second insulatinglayer 2 b stacked on the first insulating layer 2 a, a first viaconductor 6 a extending through the first insulating layer 2 a in thethickness direction, a discharge gap portion 10 provided between thefirst insulating layer 2 a and the second insulating layer 2 b so as tobe in contact with the first via conductor 6 a, a first wiring line 7 aarranged on the surface of the first insulating layer 2 a opposite tothe discharge gap portion 10 and electrically connected to the first viaconductor 6 a, and a second wiring line 7 b that is arranged on one ofthe surfaces of the second insulating layer 2 b and that includes aportion facing the first via conductor 6 a with at least the dischargegap portion 10 interposed therebetween.

The first insulating layer 2 a and the second insulating layer 2 b are,for example, ceramic layers. In the example illustrated in FIG. 1, thedischarge gap portion 10 includes a discharge auxiliary electrode 4 anda hollow 5.

With the configuration of the ESD protection device 101 in the presentembodiment, as described later, the structure of the discharge gapportion can be formed by printing with a paste. With this configuration,the thickness of the discharge gap portion can be controlled by thethickness of a layer formed by printing. The first via conductor 6 a anda second via conductor 6 b correspond to respective dischargeelectrodes. The structure of the discharge electrodes is not limited tothis, and may be any structure in which discharge electrodes face eachother with the discharge gap portion 10 interposed therebetween. The ESDprotection device 101 illustrated here has a structure in which thefirst via conductor 6 a as one discharge electrode and the second viaconductor 6 b as the other discharge electrode face each other with thedischarge gap portion 10 interposed therebetween. The details of thedischarge gap portion 10 will be described later.

The first via conductor 6 a functioning as the discharge electrode canbe formed by using a method of filling a hole with a conductive pasterather than a method of printing and, hence, can have a sufficientthickness. As a result, unlike a configuration in which a thinfilm,formed as a discharge electrode by printing, is attached, the dischargeelectrodes will not become easily detached or lost even when dischargesare repeated.

In the present embodiment, further reduction in the gap between thedischarge electrodes can be realized, and further, a problem in that thedischarge electrodes become detached can be alleviated.

As shown in the present embodiment, it is preferable that the first viaconductor 6 a have a tapered shape which is narrower on the dischargegap portion 10 side. This is due to the fact that by employing thisconfiguration, the electric charge density in the inside of the firstvia conductor 6 a can be enhanced at a side near the discharge gapportion 10 and, hence, a discharge between the discharge electrodes ismore likely to be generated. Further, due to this orientation of thetapered shape, the discharge electrode is unlikely to be detached.

As shown in the present embodiment, preferably, the ESD protectiondevice includes the second via conductor 6 b which extends through thesecond insulating layer 2 b in the thickness direction, one end of whichin the thickness direction is electrically connected to the secondwiring line 7 b, and the other end of which includes the second viaconductor 6 b in contact with the discharge gap portion 10, where thesecond via conductor 6 b faces the first via conductor 6 a with thedischarge gap portion 10 therebetween, and the second wiring line 7 b isarranged on the surface of the second insulating layer 2 b opposite tothe discharge gap portion 10. By employing this configuration, since astructure is obtained in which the discharge gap portion 10 isinterposed between two via conductors functioning as the dischargeelectrodes, a discharge between the discharge electrodes is more likelyto be generated.

As shown in the present embodiment, it is preferable that the second viaconductor 6 b have a tapered shape which is narrower at a side near thedischarge gap portion 10. This is due to the fact that by employing thisconfiguration, the electric charge density in the inside of the secondvia conductor 6 b can be enhanced at a side near the discharge gapportion 10 and, hence, a discharge between the discharge electrodes ismore likely to be generated.

As shown in the present embodiment, it is preferable that the dischargeauxiliary electrode 4 be arranged in the discharge gap portion 10. Thisis due to the fact that by employing this configuration, a discharge ismore likely to be generated due to the action of the discharge auxiliaryelectrode 4. The discharge gap portion 10 will be described in moredetail in the description of a manufacturing method which follows.

Preferably, the discharge gap portion 10 has a structure in which, inplan view, the peripheral portion is surrounded by the dischargeauxiliary electrode 4 with the hollow 5 as the center. It is preferablethat the discharge auxiliary electrode 4 contain semiconductor ceramicparticles. Further, it is preferable that the discharge auxiliaryelectrode 4 contain conductive particles coated with an insulatingmaterial. This is because a discharge is more likely to be generated atthe discharge gap portion 10 by employing this configuration.

A manufacturing method for the ESD protection device 101 illustrated inFIG. 1 will be described. FIG. 2 illustrates the state of the ESDprotection device 101 before layer stacking. The ESD protection device101 is produced by stacking a plurality of insulator sheets on top ofone another. The insulator sheets are, for example, ceramic sheets, butmay be insulator sheets of other types, not limited to ceramic sheets.The following illustrates an exemplary case in which the insulatinglayers included in the ESD protection device 101 are ceramic layers.

A hole is formed in a ceramic sheet which is to become the firstinsulating layer 2 a, and the hole is filled with a conductive paste 16a. The conductive paste 16 a is to become the first via conductor 6 alater. On the other hand, a hole is formed in a ceramic sheet which isto become the second insulating layer 2 b, and the hole is filled with aconductive paste 16 b. The orientation of a tapered shape is determinedin accordance with a surface of the sheet from which the hole is startedto be formed and, hence, the orientation of the tapered shape of afinally formed via conductor can be appropriately selected by choosingan appropriate surface from which the hole is started to be formed inthe ceramic sheet. The conductive pastes 16 a and 16 b are, for example,metal pastes.

A discharge auxiliary electrode material 14 is printed on the topsurface of the first insulating layer 2 a. A hollow-forming paste 15 isformed printed on the bottom surface. In this way, the first insulatinglayer 2 a and the second insulating layer 2 b enter the stateillustrated in FIG. 2. In the example illustrated in FIG. 2, thedischarge auxiliary electrode material 14 is printed in the shape of aring, and the hollow-forming paste 15 is printed at a position which iswithin the ring of the discharge auxiliary electrode material 14.

Note that the discharge auxiliary electrode material 14 is a materialthat can be used to form a discharge auxiliary electrode through firing.This may be, for example, insulating ceramic powder mixed withsemiconductor ceramic powder. Alternatively, the discharge auxiliaryelectrode material 14 may be formed of conductive particles coated withan insulating material. In the case of “conductive particles coated withan insulating material”, “coating” may refer to a complete coating or anincomplete coating. Coating may have a configuration in which very smallinsulating particles are attached to the surfaces of conductiveparticles. Alternatively, coating may refer to particles having acore-shell structure in which conductive particles are housed within aninsulating film. “Conductive particles” may be Cu particles. Other thanthese, particles of a conductive material such as Au, Al, Ag, or Ni maybe appropriately used. The “insulating material” with which conductiveparticles are coated may be, for example, Al₂O₃. As the “semiconductorceramic powder”, ceramic powder formed of carbide such as SiC or asemiconductor ceramic such as a transition metal oxide like MnO, NiO,CoO, or CuO may preferably be used. The semiconductor ceramic powder maybe, for example, SiC particles coated with SiO₂. The discharge auxiliaryelectrode material 14 may be a mixture of semiconductor ceramic powderand conductive particles coated with an insulating material.

The hollow-forming paste 15 is a material that can disappear at a firingtemperature. This may be a material that includes, as the main material,beads of resin that can disappear, for example, at a firing temperature.Examples of resin satisfying such a condition include acrylic resin andpolystyrene resin. The hollow-forming paste 15 can be obtained by mixingthese synthesized resin beads with, for example, binder resin and asolvent, as necessary.

The main material of the hollow-forming paste 15 is not limited toresin. Materials other than resin may be used if the materials candisappear at a firing temperature. For example, wax having a certaindegree of stiffness may be used. The main material of the hollow-formingpaste 15 is not limited to a bead-containing material. For example, aresin material containing column-shaped particles may be used, and theshape is not limited.

As illustrated in FIG. 2, an insulating layer 2 c is stacked on theunderside of the first insulating layer 2 a. An insulating layer 2 d isstacked on the upper side of the second insulating layer 2 b. In theexample illustrated here, the insulating layers 2 c and 2 d are alsoceramic sheets similarly to the first insulating layer 2 a and thesecond insulating layer 2 b.

On the top surface of the insulating layer 2 c, a conductive paste layer17 a which is to become the first wiring line 7 a later is formed inadvance. On the bottom surface of the insulating layer 2 d, a conductivepaste layer 17 b which is to become the second wiring line 7 b later isformed in advance. The conductive paste layers 17 a and 17 b can beformed by printing with a conductive paste on the surfaces of theinsulating layers.

Although it was assumed in this example that the ESD protection deviceis produced by stacking a total of four layers of ceramic sheets on topof one another, the total number of the layers is not limited to this.

As illustrated in FIG. 2, the insulating layer 2 c, the first insulatinglayer 2 a, the second insulating layer 2 b, and the insulating layer 2 dare stacked on top of one another sequentially in this order from thebottom and these layers are integrally fired. As a result, the wholedevice is unified, whereby the ESD protection device 101 illustrated inFIG. 1 is obtained.

At the time of firing, the discharge auxiliary electrode material 14becomes the discharge auxiliary electrode 4, and the hollow-formingpaste 15 disappears, thereby forming the hollow 5. At the time offiring, the conductive paste layer 17 a becomes the first wiring line 7a and the conductive paste layer 17 b becomes the second wiring line 7b.

Second Embodiment

Referring to FIG. 3, an ESD protection device in a second embodimentbased on the present disclosure will be described.

As illustrated in FIG. 3, an ESD protection device 102 in the presentembodiment has a configuration which is basically similar to that of theESD protection device 101 described in the first embodiment. In thedischarge gap portion 10, the hollow 5 has a shape which becomesnarrower toward the bottom in the ESD protection device 101 of the firstembodiment, but in the present embodiment, the hollow 5 has a shapewhich becomes narrower toward the top. In addition, in the presentembodiment, the shape of the discharge auxiliary electrode 4 is slightlydifferent from that in the first embodiment. However, also in thepresent embodiment, the discharge gap portion 10 has a structure inwhich, in plan view, the peripheral portion is surrounded by thedischarge auxiliary electrode 4 with the hollow 5 as the center.

Also in the ESD protection device 102 shown in the present embodiment,effects similar to those of the first embodiment can be obtained.

FIG. 4 illustrates the state of the ESD protection device 102 in thepresent embodiment prior to layer stacking. The present embodiment has aconfiguration similar to that illustrated in FIG. 2 of the firstembodiment. However, in the present embodiment, rather than applyingmaterials that are to form the discharge gap portion 10 to differentsurfaces through printing, both of the materials are applied to a singlesurface by printing. In other words, both of the discharge auxiliaryelectrode material 14 and the hollow-forming paste 15 are applied to thetop surface of the first insulating layer 2 a by printing. In this case,through printing, the hollow-forming paste 15 is first applied to thecenter of a location, in plan view, of the top surface of the firstinsulating layer 2 a corresponding to the top surface of the conductivepaste 16 a, and then, the discharge auxiliary electrode material 14 isapplied so as to form a ring surrounding the hollow-forming paste 15. Asillustrated in FIG. 4, the ESD protection device 102 illustrated in FIG.3 is obtained by preparing the insulating layers, stacking these layerson top of one another, and integrally firing them.

Third Embodiment

Referring to FIG. 5, an ESD protection device in a third embodimentbased on the present disclosure will be described.

As illustrated in FIG. 5, an ESD protection device 103 in the presentembodiment has a configuration which is basically similar to that of theESD protection device 102 described in the second embodiment. However,unlike the ESD protection device 102, the second via conductor 6 bprovided in the second insulating layer 2 b has a tapered shape which isoriented such that the shape becomes narrower toward the top. In otherwords, the second via conductor 6 b has a tapered shape which is widerat a side near the discharge gap portion 10.

In the present embodiment, although the degree of electric chargeconcentration at the end of the second via conductor 6 b at a sidenearer to the discharge gap portion 10 is inferior to that in the secondembodiment, a certain level of effect in an embodiment of the presentdisclosure is obtained with regard to the other points.

The ESD protection device 103 in the present embodiment can be producedby stacking a plurality of insulating layers on top of one another asillustrated in FIG. 6. In this case, the orientations of the taperedshapes of the first via conductor 6 a of the first insulating layer 2 aand the second via conductor 6 b of the second insulating layer 2 b canbe aligned. Hence, the layer stacking operations are easy because one ofthe insulating layers need not be reversed during the layer stacking.

Fourth Embodiment

Referring to FIG. 7, an ESD protection device in a fourth embodimentbased on the present disclosure will be described.

As illustrated in FIG. 7, an ESD protection device 104 in the presentembodiment has a configuration which is basically similar to that of theESD protection device 101 described in the first embodiment. However,the whole discharge gap portion 10 functions as the discharge auxiliaryelectrode 4.

Also, in the present embodiment, further reduction in the gap betweenthe discharge electrodes can be realized, and further, a problem in thatthe discharge electrodes become detached can be alleviated.

A configuration such as the one in the present embodiment can berealized by applying a sufficient amount of the discharge auxiliaryelectrode material 14 through printing to the top surface of the firstinsulating layer 2 a before layer stacking without applying ahollow-forming paste through printing. The discharge auxiliary electrodematerial 14 may be applied to the bottom surface of the secondinsulating layer 2 b by printing instead of the top surface of the firstinsulating layer 2 a. Alternatively, the discharge auxiliary electrodematerial 14 may be applied to both of the top surface of the firstinsulating layer 2 a and the bottom surface of the second insulatinglayer 2 b by printing.

Note that the configuration in which both of the discharge auxiliaryelectrode 4 and the hollow 5 are provided within the discharge gapportion 10 as shown in the first embodiment is preferable over theconfiguration in which the whole discharge gap portion 10 functions asthe discharge auxiliary electrode 4 as shown in the present embodiment,because a load on the discharge auxiliary electrode 4 can be alleviated.

Fifth Embodiment

Referring to FIG. 8, an ESD protection device in a fifth embodimentbased on the present disclosure will be described.

As illustrated in FIG. 8, an ESD protection device 105 in the presentembodiment has a configuration which is basically similar to that of theESD protection device 101 described in the first embodiment. However,the whole of the discharge gap portion 10 is the hollow 5. As shown inthe present embodiment, the discharge gap portion 10 may be the hollow5.

Also, according to the present embodiment, further reduction in the gapbetween the discharge electrodes can be realized, and further, a problemin that the discharge electrodes become detached can be alleviated.Also, in the present embodiment, a certain level of effect in thepresent disclosure can be obtained, although it is preferable to providethe discharge auxiliary electrode 4 as in the first embodiment since adischarge is more likely to be generated and, hence, a dischargestarting voltage can be lowered.

A configuration such as the one in the present embodiment can berealized by applying a sufficient amount of the hollow-forming paste 15to the top surface of the first insulating layer 2 a through printingbefore layer stacking without applying a discharge auxiliary electrodematerial through printing. The hollow-forming paste 15 may be applied byprinting to the bottom surface of the second insulating layer 2 binstead of the top surface of the first insulating layer 2 a.Alternatively, the hollow-forming paste 15 may be applied by printing toboth of the top surface of the first insulating layer 2 a and the bottomsurface of the second insulating layer 2 b.

As described in the embodiments up to here, it is preferable that thestructure in which the first via conductor 6 a and the second viaconductor 6 b face each other with the discharge gap portion 10therebetween be housed so as to be arranged in the thickness directionand so as to have a thickness smaller than the combined thickness of twoinsulating layers of the first insulating layer 2 a and the secondinsulating layer 2 b. By employing this configuration, reduction in thegap can be realized while suppressing the thickness of the whole device.Further, it is preferable that the discharge auxiliary electrode 4 bearranged in the discharge gap portion 10 in this case. According to thepresent disclosure, even the structure including the discharge auxiliaryelectrode can be housed so as to have a thickness smaller than thecombined thickness of two insulating layers.

Up to here, configurations that include the second via conductor 6 b inaddition to the first via conductor 6 a have been described. However,the second via conductor 6 b is not essential to the present disclosure.Next, an embodiment without the second via conductor 6 b will bedescribed.

Sixth Embodiment

Referring to FIG. 9, an ESD protection device in a sixth embodimentbased on the present disclosure will be described.

As illustrated in FIG. 9, an ESD protection device 106 in the presentembodiment includes a first insulating layer 2 a, a second insulatinglayer 2 b stacked on the first insulating layer 2 a, a first viaconductor 6 a extending through the first insulating layer 2 a in thethickness direction, a discharge gap portion 10 provided between thefirst insulating layer 2 a and the second insulating layer 2 b so as tobe in contact with the first via conductor 6 a, a first wiring line 7 aarranged on the surface of the first insulating layer 2 a opposite tothe discharge gap portion 10 of the first insulating layer 2 a andelectrically connected to the first via conductor 6 a, and a secondwiring line 7 b that is arranged on one of the surfaces of the secondinsulating layer 2 b and that includes a portion facing the first viaconductor 6 a with at least the discharge gap portion 10 interposedtherebetween.

The phrase “a second wiring line 7 b that is arranged on one of thesurfaces of the second insulating layer 2 b” means that when the secondvia conductor 6 b is provided so as to extend through the secondinsulating layer 2 b, as shown in the first to fifth embodiments, thesecond wiring line 7 b may be provided on the top surface of the secondinsulating layer 2 b, but when the second via conductor 6 b does notexist in the second insulating layer 2 b, as shown in the presentembodiment, the second wiring line 7 b is provided on the bottom surfaceof the second insulating layer 2 b. In other words, the second wiringline 7 b is provided on the bottom surface of the second insulatinglayer 2 b at least in the present embodiment.

In the present embodiment, the first via conductor 6 a and the secondwiring line 7 b correspond to respective discharge electrodes. The ESDprotection device 106 illustrated here has a structure in which thefirst via conductor 6 a as one discharge electrode and the second wiringline 7 b as the other discharge electrode face each other with thedischarge gap portion 10 interposed therebetween.

The details of the discharge gap portion 10 may be determined on thebasis of any concept described in the first to fifth embodiments.

Also, according to the present embodiment, further reduction in the gapbetween the discharge electrodes can be realized, and further, a problemin that the discharge electrodes become detached can be alleviated.

As shown in the first to fifth embodiments, when a configuration isemployed in which the second via conductor 6 b is provided so as toextend through the second insulating layer 2 b and is made to functionas a discharge electrode, and in which via conductors face each other,it is easy for the electric charges to be concentrated at the tip of thevia conductor by utilizing the shape of the via conductor protruding inthe thickness direction and, hence a discharge is more likely to begenerated. In other words, this configuration is preferable since astarting voltage can be easily lowered. However, even with theconfiguration in which the via conductor exists only on the one side ofthe discharge gap portion as shown in the present embodiment, a certainlevel of effect in the present disclosure can be obtained.

The ESD protection device 106 in the present embodiment can be producedby stacking a plurality of insulating layers on top of one another asillustrated in FIG. 10. In this case, there is no need to make a hole inthe second insulating layer 2 b or fill it with a conductive paste.Hence, this is favorable from the viewpoint of reducing the number ofprocesses.

Example Experiments

To examine the discharge responsiveness to ESD, a plurality of types ofESD protection devices based on the present disclosure and an existingtechnology were prepared as samples I-V, and an electrostatic dischargeimmunity test was performed, which is defined in IEC61000-4-2 that is atype of International Electromechanical Commission (IEC) standards.

Sample I is the ESD protection device 101 shown in the first embodiment.

Sample II is the ESD protection device 102 shown in the secondembodiment.

Sample III is the ESD protection device 103 shown in the thirdembodiment.

Sample IV is the ESD protection device 106 shown in the sixthembodiment.

Sample V, which is an ESD protection device based on an existingtechnology, is an ESD protection device 100 illustrated in FIG. 11. TheESD protection device 100 is formed by stacking ceramic layers asinsulating layers. The ESD protection device 100 includes a first wiringline 7 a and a second wiring line 7 b. The tip of the first wiring line7 a and the tip of the second wiring line 7 b face each other with theinternal space of a through hole 9 therebetween. The structureillustrated in FIG. 11 was obtained by stacking insulating layers on topof one another, as illustrated in FIG. 12. In other words, an insulatinglayer 2 f including a through hole 9 formed therein was prepared, andwas arranged so as to be interposed between insulating layers 2 c and 2d on which conductive pastes 17 a and 17 b were respectively applied byprinting. Further, an insulating layer 2 e including nothing formedtherein was stacked on top of the insulating layer 2 d, and the total offour layers were integrally fired. In this way, the ESD protectiondevice 100 illustrated in FIG. 11 was obtained.

As an electrostatic discharge immunity test, it was determined whetheror not a discharge is generated between the discharge electrodes of asample by applying a voltage of 8 kV through a contact discharge. It canbe determined whether or not a discharge has been generated between thedischarge electrodes of a sample by determining whether or not a voltageis applied to a protected circuit. The level of a discharge startingvoltage between the discharge electrodes of the sample can be determinedon the basis of a peak voltage detected by the protected circuit. Thesmaller the peak voltage detected by the protected circuit, the betterthe function of the sample.

The evaluation results are represented as follows.

The case in which the peak voltage is below 350 V is ranked “A”, whichmeans excellent.

The case in which the peak voltage is 350 V or higher and below 500 V isranked “B”, which means good.

The case in which the peak voltage is 500 V or higher and below 600 V isranked “C”.

The case in which the peak voltage is higher than 600 V is ranked “D”,which means poor.

The evaluation results are illustrated in the “ESD dischargeresponsiveness” column of Table 1.

TABLE 1 Table of evaluation results ESD discharge ESD repetition OverallSample responsiveness endurance judgment Sample I A A Excellent SampleII A A Excellent Sample III A B Good Sample IV B C Fair Sample V C DPoor (Comparative example)

Further, to examine the repetition endurance for ESD, a voltage of 8 kVwas applied to the input terminal 503 one hundred times through contactdischarge, and after this, the discharge responsiveness was checkedagain by using the electrostatic discharge immunity test. The evaluationresults at this time are shown in column “ESD repetition endurance” ofTable 1.

Overall judgment was determined on the basis of two evaluation results,i.e., ESD discharge responsiveness and ESD repetition endurance, and wasranked in four stages: excellent, good, fair, and poor.

As illustrated in Table 1, samples I-III were favorable particularly interms of discharge responsiveness in the initial state. In addition,samples I and II were favorable particularly in terms of repetitionendurance. Hence, samples I and II were ranked “excellent” in overalljudgment.

Sample III was favorable particularly in terms of dischargeresponsiveness in the initial state, but was inferior to samples I andII in terms of repetition endurance. Hence, sample III was ranked “good”in overall judgment. It can be said that sample III is excellent next tosamples I and II.

Sample IV, which is “fair” in overall judgment, is inferior to samplesI-III, but is excellent compared with sample V based on an existingtechnology and, hence, it can be said that a certain level of effect inthe present disclosure is obtained also in this case.

Sample V, although the discharge responsiveness was below 600 V in theinitial state, was not acceptable in terms of repetition endurance and,hence, was ranked “poor” in overall judgment.

The descriptions of the above embodiments are examples in all therespects and are not restrictive. The scope of the present disclosure isshown by the claims and not by the embodiments described above, andincludes all the modifications having equivalent meaning and within thescope of the claims.

The present disclosure can be utilized in an ESD protection device.

2 a first insulating layer, 2 b second insulating layer, 2 c, 2 d, 2 einsulating layers, 4 discharge auxiliary electrode, 5 hollow, 6 a firstvia conductor, 6 b second via conductor, 7 a first wiring line, 7 bsecond wiring line, 10 discharge gap portion, 14 discharge auxiliaryelectrode material, 15 hollow-forming paste, 16 a, 16 b conductivepaste, 17 a, 17 b conductive paste layers, 91, 92 arrows, 100 ESDprotection device (based on an existing technology), 101, 102, 103, 104,105, 106 ESD protection devices, 501 (general) ESD protection device,502 protected circuit, 503 terminal

The invention claimed is:
 1. An ESD protection device comprising: afirst insulating layer; a second insulating layer stacked on the firstinsulating layer; a first via conductor extending through the firstinsulating layer in a thickness direction; a discharge gap portionprovided so as to be in contact with the first via conductor, betweenthe first insulating layer and the second insulating layer; a firstwiring line arranged on a surface of the first insulating layer oppositeto the discharge gap portion and electrically connected to the first viaconductor; and a second wiring line arranged on one surface of thesecond insulating layer and including a portion facing the first viaconductor with at least the discharge gap portion interposedtherebetween.
 2. The ESD protection device according to claim 1, whereinthe first via conductor has a tapered shape narrower at a side near thedischarge gap portion.
 3. The ESD protection device according to claim1, further comprising: a second via conductor extending through thesecond insulating layer in the thickness direction, wherein one end ofthe second via conductor in the thickness direction is electricallyconnected to the second wiring line, and the other end of the second viaconductor is connected to the discharge gap, wherein the second viaconductor faces the first via conductor with the discharge gaptherebetween, and wherein the second wiring line is arranged on asurface of the second insulating layer opposite to the discharge gapportion.
 4. The ESD protection device according to claim 3, wherein thesecond via conductor has a tapered shape narrower at a side near thedischarge gap portion.
 5. The ESD protection device according to claim1, wherein the discharge gap portion is a hollow.
 6. The ESD protectiondevice according to claim 1, wherein a discharge auxiliary electrode isarranged in the discharge gap portion.
 7. The ESD protection deviceaccording to claim 1, wherein the discharge gap portion includes astructure having, in plan view, a peripheral portion surrounded by adischarge auxiliary electrode with a hollow as a center.
 8. The ESDprotection device according to claim 6, wherein the discharge auxiliaryelectrode comprises semiconductor ceramic particles.
 9. The ESDprotection device according to claim 6, wherein the discharge auxiliaryelectrode comprises conductive particles coated with an insulatingmaterial.
 10. The ESD protection device according to claim 3, wherein astructure having the first via conductor and the second via conductorfaced each other with the discharge gap portion therebetween is housedso as to be arranged in the thickness direction and so as to have athickness smaller than a combined thickness of two insulating layers ofthe first insulating layer and the second insulating layer.
 11. The ESDprotection device according to claim 10, wherein a discharge auxiliaryelectrode is arranged in the discharge gap portion.